1. Field of the Invention
This invention relates to metallic fibers and more particularly to an improved method of making fine and ultra fine metallic fibers through a new cladding and drawing process.
2. Background of the Invention
In recent years, the need for high quality, small diameter metallic fibers has grown as new applications for such fibers are developed by the art. High quality, small diameter metallic fibers have been used in diverse applications such as filtration media as well as being dispersed within a polymeric material to provide electrostatic shielding for electronic equipment and the like. This need for high quality, small diameter metallic fibers has produced various new ways and processes for making these high quality metallic fibers for the various uses in the art.
Typically, high quality metallic fibers may be characterized as small diameter metallic fibers having a diameter of less than 50 micrometers with a substantially uniform diameter along the longitudinal length thereof. Typically, the fibers are produced in a fiber tow and severed to have a longitudinal length at least 1,000 times the diameter of the metallic fiber.
The metallic fibers as set forth herein are typically manufactured by cladding a metallic wire with a cladding material to provide a first cladding. The first cladding is drawn and annealed for reducing the diameter of the first cladding. A plurality of the first claddings are clad to provide a second cladding. The second cladding is subjected to a multiple drawing and annealing process for reducing the diameter of the second cladding and the corresponding diameter of the first claddings contained therein. Depending upon the desired end diameter of the first cladding, the plurality of second claddings may be clad to provide a third cladding. Multiple drawings of the third cladding reduces the diameter of the first and second claddings to provide metallic fibers within the first claddings of the desired diameter. After the desired diameter of the metallic fibers within the first cladding is achieved, the cladding materials are removed by either an electrolysis or a chemical process thereby providing metallic fibers of the desired final diameter.
Ideally, the metallic fibers are made of a stainless steel and are produced by a drawing process. The drawing process comprises cladding a stainless steel wire with a cold roll steel clad material to produce a first cladding. The first cladding is subjected to a series of drawing and annealing processes for reducing the diameter thereof. Thereafter, a plurality of the first claddings are encased within a second cladding material such as cold roll steel for producing a second cladding. The second cladding is subjected to a series of drawing and annealing processes for further reducing the diameter of the second cladding. After the second drawing process, the original wires of the first cladding are reduced to a diameter of 10 to 50 microns that is suitable for some applications. For applications requiring finer metallic fibers, a plurality of second claddings are clad with a third cladding material to provide a third cladding. Third cladding is subjected to a series of drawing and annealing for further reducing the diameter of the original metallic wires. A triple cladding process can produce final wires having a diameter of as low as 6 microns in diameter.
The cladding material is removed by subjecting the finally drawn cladding to an acid leaching process whereby the acid dissolves the cladding material leaving the metallic fibers. The metallic fibers may be severed to produce metallic sliver or cut metallic fibers or may be used as metallic fiber tow.
Although the foregoing process of making fine metallic fibers has been found satisfactory in the prior art, the process has certain disadvantages for some applications. The first disadvantage is the requirement of incorporating a three cladding process in order to produce metallic fibers in the range of 6 microns in diameter. Another limitation is the initial diameter of the metallic wire must be of a sufficient size in order to clad carbon steel thereto. Another disadvantage of the aforementioned process includes the incomplete removal of the cladding material from the metallic fibers during the leaching process.
Another disadvantage of this prior art process is the diffusion of impurities of the carbon steel into the metallic fibers during the drawing process. A substantial amount of heat and pressure are produced during the drawing process causing a fusion of undesirable materials from the carbon steel upon the surface of the metallic fibers. These undesirable materials such as carbon, hydrocarbon materials such as oils and the like remain on the surface of the metallic fibers through the leaching process and reside thereon in the end product. In certain applications, these undesired impurities are detrimental to the application and the use of the metallic fibers. For example, these undesirable impurities may be detrimental when the metallic fibers are used in a filtration process or the like.
Some of the prior art have attempted to use copper as a cladding material for producing fine metallic fibers. U.S. Pat. No. 2,050,298 to Everett discloses a method for producing filaments from a rod, which comprises the steps of bundling the rods side by side in a matrix, drawing the bundle, removing the matrix, and separating the wires. The matrix serves to separate the elements, limiting distortion during drawing and preventing adjacent elements from becoming attached to each other. Two embodiments of matrix material given are metal powder and individual metal sheaths, or a combination of the two. The sheath may be dissolved off with acid. An example given consisted of stainless steel fibers having a copper matrix and a tubular casing of high carbon steel, the removal of which was effected by a hot acid bath. An alternative method for stainless steel fibers consisted of encasing the fibers in separate copper tubes and then packing a number of these in a copper tube.
U.S. Pat. No. 2,077,682 discloses a process for the production of fine wires, strips, thin sheets or the like by reduction from elements of larger cross-section which comprises assembling inside a tubular casing a plurality of metal elements composed of alloy steel comprising 0.05% to 0.20% carbon, 6% to 14% nickel and 10% to 20% chromium, and subjecting the encased elements as a unit to reducing operations to reduce the cross-section area of all the elements, simultaneously, and then removing the casing.
U.S. Pat. No. 3,066,384 discloses a method of making from 80" wide to 160" wide thin sheets of a metal which is difficult to roll selected from the group consisting of stainless steel, ferrous alloys, titanium, zirconium and their alloys, which consists in assembling a pack of plates of the metal with weld-preventing material therebetween, placing the pack within a box welded up from steel top and bottom plates and steel side and end bars with the top and bottom plates overlapping the side and end bars, providing vent holes in all of the bars, hot rolling the resulting pack-in-a-box first by cross rolling and then by rolling longitudinally, thereby reducing the first-mentioned plates to sheets, then subjecting the sheets while still confined within the box to heating and cooling stages in predetermined order thereby developing desired physical properties in the sheets, roller leveling the hot-rolled pack while still in the box, and then opening the box and removing and separating the sheets.
U.S. Pat. No. 3,204,326 discloses a method of making a fused energy-conducting structure having a multiplicity of juxtaposed long and thin energy-conducting guides extending from one end toward the other end thereof utilizing a rolling mill, the method comprising the steps of placing a multiplicity of energy-conducting fibers each clad with a glass having a relatively low softening temperature and coefficient of expansion in side-by-side bundled relationship longitudinally within a tubular supporting member formed of a metal having a substantially higher softening temperature and coefficient of expansion than the glass, the fibers being in such number and of such diameter as to substantially fill the supporting member, there being undesired interstices containing air and gases extending longitudinally between the fibers, heating the assembly of the supporting member and fibers to a temperature sufficient to soften and fuse claddings together and rolling the heated assembly under compression progressively from one end toward the other end thereof to a reduced cross-sectional size, the reduction in size being of an amount at least sufficient to effect substantially complete closure of the interstices progressively along the length of the assembly and simultaneous longitudinal extrusion of air and gases therein immediately prior to adjoining and fusion of portions of the claddings along the interstices as the assembly is rolled.
U.S. Pat. No. 3,277,564 discloses a method of forming a tow of substantially bare filaments comprising the steps of sheathing each of a plurality of elongated drawable metal elements from which the filaments are to be formed with a tubular sheath formed of a material having characteristics permitting the sheaths to be pressed together to form a substantially monolithic body and differing chemically substantially from those of the elements to permit separation of the sheath material from elements. The sheathed elements are bundled in a substantially parallel relationship. The bundled sheathed elements are mechanically worked in at least one working step to reduce the cross-section of the elements to a preselected filament cross-section of less than approximately 10 microns maximum transverse dimension and to cause the sheath material to form a matrix extending substantially continuously in cross-section thereby to preclude separation of individual sheathed filaments. The sheathing material is substantially completely removed while maintaining the filaments in bundled relationship to provide a tow of substantially bare separate filaments.
U.S. Pat. No. 3,378,916 discloses a method of process for the production of superconducting niobium-zirconium alloy wire comprising heat-treating a niobium-zirconium material containing a second phase constituent and having a substantially non-dendritic refined crystal structure substantially free of high concentrations of impurities, in a temperature range of 1000.degree.-1250.degree. C. under inert conditions for 30-120 minutes, whereby the second phase is placed in solution with the material. The process includes quenching the material as quickly as possible to retain the second-phase constituents in solution and working the material at a temperature below 500.degree. C. to reduce its cross section and removing any surface defects which may be present. The material is heat-treated at a temperature in the range of 750.degree. C.-825.degree. C. under inert conditions for 15-130 minutes and is enclosed within a sheath of different material having substantially similar working properties to the material regarding ductility, rate of work-hardening and hardness. The material is deformed within the sheath together to the required final cross-section of the material. The sheath is dissolved and the material is copper plated.
U.S. Pat. No. 3,394,213 discloses a method of forming fine filaments, such as filaments of under approximately 15 microns, in long lengths wherein a plurality of sheathed elements are firstly constricted to form a reduced diameter billet by means of hot forming the bundled filaments. After the hot forming constriction, the billet is then drawn to the final size wherein the filaments have the desired final small diameter. The material surrounding the filaments is then removed by suitable means leaving the filaments in the form of a tow.
U.S. Pat. No. 3,503,200 to Roberts et al. provides a method of forming a twisted bundle of filaments wherein a plurality of sheathed filaments are bundled together, sheathed or embedded in a matrix, and constricted by being drawn through a constricting die. Then the bundle is fed onto a roll, with a twist imparted to the filaments at the same time.
U.S. Pat. No. 3,540,114 discloses a method of forming fine filaments formed of a material such as metal by multiple end drawing a plurality of elongated elements having thereon a thin film of lubricant material. The plurality of elements may be bundled in a tubular sheath formed of a drawable material. The lubricant may be applied to the individual elements prior to the bundling thereof and may be provided by applying the lubricant to the elements while they are being individually drawn through a coating mechanism such as a drawing die. The lubricant comprises a material capable of forming a film having a high tenacity characteristic whereby the film is maintained under the extreme pressure conditions of the drawing process. Upon completion of the constricting operation, the tubular sheath is removed. If removed, the lubricant may also be removed from the resultant filaments.
U.S. Pat. No. 3,550,247 discloses carbon filaments being coated with a metal by electrodeposition, electroless plating or chemical plating. Preferably the carbon filaments are subjected to an oxidizing treatment under strong oxidizing conditions before being coated with the metal. Metal coated filaments are incorporated in the metal matrix by electroforming, powder technology techniques, casting or by subjecting the coated filaments to a combination of heat and pressure to coalesce them into a composite material.
U.S. Pat. 3,596,349 discloses a method of fabricating a unitary superconducting multistrand conductor. The method includes coating a plurality of fine superconducting wires with a normal metal having ductility characteristics similar with those of the superconducting metal, assembling the coated wires in a close-packed array, and swagging the array so that the metal coatings of the wires form a conductive continuous matrix in which the wires are solidly embedded.
U.S. Pat. No. 3,762,025 discloses a process for producing long continuous lengths of metallic filaments which comprises securing four flat plates of a first metal to each of the elongated sides of a billet of a second metal and having a cross section in shape of a rectangle, by edge welding each of the plates. The resulting assembly is essentially void free. The rectangular cross section of the billet is reduced while being elongated by hot rolling. The resulting elongated rectangular structure, having a core of the second metal and a cladding of the first metal over the elongated sides, is divided into a plurality of elements of the same lengths. The elements are inserted into a hollow metal tube open at both ends having a rectangular cross section in a manner to essentially eliminate the voids and with their longitudinal axes and the longitudinal axis of the tube essentially parallel. Ends of the tube are sealed and the sealed unit is reduced in cross section and elongated by hot rolling. The other materials are removed from the resulting filaments of the first metal yielding materials suitable for weaving into metal cloth.
U.S. Pat. No. 3,785,036 discloses a method of producing fine metallic filaments by covering a bundle of a plurality of metallic wires with an outer tube metal and drawing the resultant composite wire, wherein the outer tube metal on both sides of the final composite wire obtained after the drawing step is cut near to the core filaments present inside the outer tube and then both uncut surfaces of the composite wire are slightly rolled thereby to divide the outer tube metal of the composite wire continuously and thus separating the outer tube metal from fine metallic filaments. The separation treatment can be effected by a simple apparatus within a short time This reduces the cost of production, and enables the outer tube metal to be recovered in situ.
U.S. Pat. No. 3,807,026 discloses a method of producing a yarn of fine metallic filaments at low cost, which comprises covering a bundle of a plurality of metal wires with an outer tube metal to form a composite wire, drawing the composite wire and then separating the outer tube metal from the core filaments in the composite wire, wherein for ease of the separation treatment, the surfaces of the metal wires are coated with a suitable separator or subjected to a suitable surface treatment before the covering of the outer tube metal, thereby to prevent the metallic bonding of the core filaments to each other in the subsequent drawing or heat-treatment of the composite wire.
U.S. Pat. No. 4,044,447 discloses a number of wires gathered together and bound with an armoring material in the shape of a band. The wires in this condition are drawn by means of a wire drawing apparatus having dies and a capstan. A plurality of bundles of such wires are gathered together and bound in the same way as in the foregoing to form a composite bundle body, which is further drawn, and these processes are repeated until at least filaments of a specific diameter are obtained in quantities.
U.S. Pat. No. 4,065,046 discloses a collimated hole structure formed by constricting a plurality of tubular elements each provided with a core for supporting the tubular element during the constricting operation. The bundle of elements is constricted to a point where the elements effectively fuse into a substantially monolithic body. The cores are then removed, leaving a plurality of extremely small diameter, generally parallel passages in a solid body. The tubular elements may be arranged in any desired array, and thus the passages may be provided similarly in any desired array. The passages may have high aspect ratios and may be closely juxtaposed. In one illustrative application, the collimated hole structure is provided with dielectric film and utilized as an anode portion of an electrolytic capacitor. In another illustrative application, the collimated hole structure is utilized as a tip for a drilling device.
U.S. Pat. No. 4,118,845 discloses a method of forming a tow of filaments and the two formed by the method wherein a bundle of elongated elements such as rods or wires, is clad by forming a sheath of material different from that of the elements about the bundle and the bundle is subsequently drawn to constrict the elements to a desired small diameter. The elements may be formed of metal. The bundle may be annealed, or stress relieved, between drawing steps as desired. The sheath may be formed of metal and may have juxtaposed edges thereof welded together to retain the assembly. The sheath is removed from the final constricted bundle to free the filaments in the form of tow.
U.S. Pat. No. RE 28,526 to Ziemek discloses a copper band formed around an aluminum core wire and the single seam in the sheath material is welded without bonding of the sheath and core, care being taken that all surfaces are clean and maintained free of oxides. The copper tube, is reduced to the diameter of the aluminum core. This composite wire is then passed through a plurality of drawing dies which reduce the diameter of the wire, preferably at least 50 percent, care being taken to prevent the copper sheath from tearing. The drawing operation produces, depending on the reduction rate, an initial or a complete bond between the core and sheath. Subsequently, the clad wire is either subjected to a limited diffusion heat treatment, conditions of the heat treatment being controlled to produce a complete and flawless bond between the sheath and core but, at the same time, avoiding the formation of an CuAl.sub.2, a phase which is brittle or is annealed to get the required grade. Generally, the diffusion layer on either side of the sheathcore interface is limited to about 10.mu..
U.S. Pat. No. 3,277,564 to Webber et al teaches a method of forming a tow of substantially bare filaments comprising the steps of sheathing each of a plurality of elongated drawable metal elements from which the filaments are to be formed with a tubular sheath formed of a material having characteristics permitting the sheaths to be pressed together to form a substantially monolithic body and differing chemically substantially from those of the elements to permit separation of the sheath material from elements when desired. The sheathed elements are bundled in substantially parallel relationship. The bundled sheathed elements are mechanically worked in at least one working step to reduce the cross-section of the elements to a preselected filament cross-section of less than approximately 10 microns maximum transverse dimension and to cause the sheath material to form a matrix extending substantially continuously in cross-section thereby to preclude separation of individual sheathed filaments. The sheathing material is completely removed while maintaining the filaments in bundled relationship to provide a tow of substantially bare separate filaments.
U.S. Pat. No. 3,375,569 to Eichinger et al teaches a method of making porous structures comprising the steps of winding a first row of wire on a winding support, the row having a large number of wire turns therein and having a predetermined pitch, winding subsequent rows of wire on the first row with each subsequent row having the same pitch as the first row so that each of the wire turns contacts substantially all of the immediately adjacent ones of the wire turns, bonding each of the turns to substantially all of its adjacent turns, and cutting sections from the turns generally transversely of the winding direction, the sections corresponding in thickness to the desired thickness of the porous structures.
U.S. Pat. No. 3,894,675 to Klebl et al discloses a copper clad steel wire being continuously produced by forming a copper sheet into a tube around the wire and welding the copper tube, at the edges, to produce a longitudinal seam. The diameter of the welded copper tube is reduced to the diameter of the wire, and the composite heated to a temperature of at least 850.degree. C., at which temperature the cross sectional area of the composite wire is reduced by at least 10 percent to bond the copper to the steel wire.
U.S. Pat. No. 3,945,555 Schmidt discloses a manufacturing process for a solid or hollow shaft consisting of aluminum or titanium with beryllium reinforcing therein. Beryllium rods are either clad with aluminum or titanium or, in the alternative, holes are drilled in an aluminum or titanium block which beryllium material is thereafter inserted into the holes. The preform with a hard steel central mandrel around which the beryllium rods are positioned is placed within a steel can and heated to a predetermined temperature. Pressure is then uniformly applied to the outer circumference of the can to ensure uniform deformation of the beryllium reinforcement. The uniform exterior pressure on the outer surfaces of the beryllium rods and the interior pressure on these rods caused by the hard steel mandrel against the under surfaces of the rods as a result of a reduction process causes the beryllium rods to assume an arcuate ribbon configuration. For hollow shafting, the mandrel at the center of the preform may later be removed.
U.S. Pat. No. 4,109,870 to Wolber discloses a multiorifice structure and a method of making the multiorifice structure. The structure is made by fusing a plurality of parallel rods stacked in a regular geometric pattern. The interstices between the fused rods form a plurality of small orifices of a noncircular configuration which are ideally suited for atomizing a pressurized fluid. In the preferred embodiment, the multiorifice structure is a fuel atomizer for atomizing the fuel ejected from an automotive type fuel injection valve.
U.S. Pat. No. 4,156,500 to Yoshida et al teaches a method of producing a copper clad steel wire comprising the steps of preparing a 5 to 15 mm diameter steel rod and a 21 to 66.7 mm width copper tape; continuously supplying the steel rod and the copper tape separately and cleaning the surfaces thereof; forming the copper tape in tubular form such that the copper tape can cover the steel rod while supplying the steel rod and the copper tape in parallel, and welding the edges of the copper tape in a non-oxidizing atmosphere; sinking the tubular copper tape sufficiently for the copper tape to substantially come into contact with the steel rod to form a copper clad steel rod; cold-drawing the copper clad steel rod and/or hot working the clad rod at a temperature of 400.degree. to 800.degree. C. to reduce its cross-sectional area by more than 20%; and then annealing the copper clad steel rod at a temperature of 300.degree. to 1050.degree. C.
U.S. Pat. No. 4,166,564 to Wolber discloses a multiorifice structure and a method of making the multiorifice structure. The structure is made by fusing a plurality of parallel rods stacked in a regular geometric pattern. The interstices between the fused rods form a plurality of small orifices of a noncircular configuration which are ideally suited for atomizing a pressurized fluid. In the preferred embodiment, the multiorifice structure is a fuel atomizer for atomizing the fuel ejected from an automotive type fuel injection valve.
Although the aforementioned processes have provided high quality metallic fibers in the desired diameter range, the aforementioned processes still suffer from certain deficiencies. Firstly, the process of multiple claddings in one example incorporates the use of carbon steel cladding of stainless steel fibers. Unfortunately, the removal of carbon steel cladding material from stainless steel wire or fibers is a costly, time consuming and an environmentally unfriendly process. This is especially true when a three clad process is incorporated into the process of making fine metallic fibers.
Another disadvantage of the aforementioned process when making stainless steel fibers through the use of a carbon steel cladding is the involved chemical process for removing the carbon steel cladding from the stainless steel fibers. A further disadvantage of the prior art process is the amount of unusable byproducts from the carbon steel removed from the stainless steel to produce the fine metallic fibers.
Accordingly, it is an object of the present invention to provide an improved process for making fine metallic fibers which overcomes the disadvantages of the prior art and produces fine and ultra metallic fibers in an economic and efficient manner.
Another object of this invention is to provide an improved process for making fine and ultra fine metallic fibers wherein the cladding is used only partially through the drawing process.
Another object of this invention is to provide an improved process for making fine and ultra fine metallic fibers incorporating only a single continuous cladding process or a multiple continuous cladding process.
Another object of this invention is to provide an improved process for making fine and ultra metallic fibers wherein the cladding of the formed type is mechanically removed without the need for a chemical leaching process.
Another object of this invention is to provide an improved process for making fine and ultra fine metallic fibers incorporating a metallic copper coating and a carbon steel cladding wherein the copper coating inhibits the diffusion of undesirable impurities from the carbon steel cladding into the metallic fibers.
Another object of this invention is to provide an improved process for making fine and ultra fine metallic fibers wherein the metallic fibers can be produced with a simple chemical leaching process or electrolysis process whereby the material removed is totally reusable within the process.
Another object of this invention is to provide an improved process for making fine and ultra fine metallic fibers whereby the leaching or electrolysis process is simple and efficient, fast and economical to operate.
Another object of this invention is to provide an improved process for making fine and ultra fine metallic fibers whereby fibers in the nanometer range can be obtained in commercial quantities.
Another object of this invention is to provide an improved process for making fine and a fine metallic fibers that provides high quality metallic fibers of low impurities at an economical manufacturing cost.
Another object of this invention is to provide an improved process for making fine and ultra fine metallic fibers that incorporates a process that produces only products that may be reusable byproducts or environmentally safe disposable byproducts.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed as being merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the invention. Accordingly other objects in a full understanding of the invention may be had by referring to the summary of the invention, the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.